The present invention relates to methods and compositions for using acidic treatment fluids that comprise an acid fluid and an ester-containing quaternary ammonium compound (“esterquat”). More particularly, the present invention relates to methods of using such acidic treatment fluids in acidic subterranean treatments as corrosion inhibitors, sludge reducers, and compounds capable of inhibiting the formation of emulsions or reducing the existence of emulsions.
Acidic treatment fluids are commonly used in subterranean operations. One such acidic operation is an acidizing stimulation treatment in which subterranean formations are treated with acid fluids to stimulate the production of hydrocarbons. Such acid stimulation treatments often may be carried out as “matrix acidizing” processes or as “fracture acidizing” processes. In typical matrix acidizing processes, an acidizing treatment fluid is injected from the well bore into the formation at a rate and pressure below that which is sufficient to create a fracture therein. The acid permeates into formation pores and dissolves materials that clog or constrict them, thereby hopefully increasing the formation's permeability. In fracture acidizing, an acidizing treatment fluid is injected into the subterranean formation at a pressure sufficient to create or enhance at least one fracture therein. In such operations, the permeability of the formation may be enhanced. Using acidic treatment fluids in subterranean operations is sometimes problematic. Three primary problems often encountered with the use of acid fluids are equipment corrosion, undesirable emulsion formation, and sludge formation.
Corrosion can act to greatly limit the life of subterranean equipment, piping, and casing materials. Moreover, metal corrosion can increase the level of heavy metals in fluids transmitted through the corroded equipment, potentially increasing the environmental impact of those fluids when they are disposed of or further processed. The expense associated with repairing or replacing corrosion damaged metal tubular goods and equipment can be very high. In a well treatment using an aqueous acid solution, the corrosion of metal surfaces in tubular goods and equipment may result in at least the partial neutralization of the aqueous acid solution before it reacts with acid-soluble materials in the subterranean formation to be treated, which is undesirable. Also, if crude oil should contact the dissolved metals in the acid fluids, precipitation of insoluble sludge may result that can severely damage the permeability of the subterranean formation.
Acids may react with oils in the formation and form insoluble films, the coalescence of which creates “sludge.” Typically, such sludge includes asphaltenes, resins, paraffins, and other complex hydrocarbons. Additionally, oil and aqueous fluids used in the well (including any acidizing fluids) may form emulsions that undesirably increase the viscosity of the fluid, and thereby increase the power required to pump the oil to the surface. Moreover, the produced hydrocarbons and the acid must generally be separated for sale, and where an emulsion has formed such separation may be more difficult.
A variety of corrosion inhibiting, anti-sludge, and anti-emulsion formulations for use in acid fluids have been developed and used successfully. Many of such corrosion inhibiting formulations have included quaternary ammonium compounds (“quats”) as essential components, particularly in high temperature applications. Quats bear a positive charge and, therefore, effectively coat a negatively charged layer of a metallic surface. However, because of environmental concerns their usage is being curtailed.
Ester-containing normal quaternary ammonium compounds (“esterquats”) have been developed in recent years for use as ecologically friendly surfactants in the personal care products, as detergents, and fabric softeners. Esterquats have been shown useful in reducing corrosion and sludge and in inhibiting the formation or reducing the existence of emulsions in personal care products. These compounds are easily biodegraded in alkaline environments and exhibit low fish toxicity upon degradation. For at least these reasons, they have largely replaced alkyl quats in the detergent industry.